<template>
	<div class="progress-bar" ref="progressBar" @click="progressClick">
		<div class="bar-inner">
			<div class="progress" ref="progress"></div>
			<div class="progress-btn-wrapper" ref="progressBtn"
				@touchstart.prevent="progressTouchStart"
				@touchmove.prevent="progressTouchMove"
          		@touchend="progressTouchEnd"
			>
				<div class="progress-btn"></div>
			</div>
		</div>
	</div>
</template>

<script type="text/ecmascript-6">
	import {prefixStyle} from 'common/js/dom'

  	const progressBtnWidth = 16
  	const transform = prefixStyle('transform')
  	
	export default {
		props: {
      		percent: {
        		type: Number,
        		default: 0
      		}
    	},
	    created() {
	      	this.touch = {}
	    },
	    methods: {
	      	progressTouchStart(e) {
		        this.touch.initiated = true
		        this.touch.startX = e.touches[0].pageX
		        this.touch.left = this.$refs.progress.clientWidth
	      	},
	      	progressTouchMove(e) {
		        if (!this.touch.initiated) {
		          	return
		        }
		        const deltaX = e.touches[0].pageX - this.touch.startX
		        const offsetWidth = Math.min(this.$refs.progressBar.clientWidth - progressBtnWidth, Math.max(0, this.touch.left + deltaX))
		        this._offset(offsetWidth)
	      	},
	      	progressTouchEnd() {
		        this.touch.initiated = false
		        this._triggerPercent()
	      	},
	      	progressClick(e) {
		        const rect = this.$refs.progressBar.getBoundingClientRect()
		        const offsetWidth = e.pageX - rect.left
		        this._offset(offsetWidth)
		        // 这里当我们点击 progressBtn 的时候，e.offsetX 获取不对
//		        this._offset(e.offsetX)
		        this._triggerPercent()
	      	},
	      	_triggerPercent() {
		        const barWidth = this.$refs.progressBar.clientWidth - progressBtnWidth
		        const percent = this.$refs.progress.clientWidth / barWidth
		        this.$emit('percentChange', percent)
	      	},
	      	_offset(offsetWidth) {
		        this.$refs.progress.style.width = `${offsetWidth}px`
		        this.$refs.progressBtn.style[transform] = `translate3d(${offsetWidth}px,0,0)`
	      	}
	    },
	    watch: {
	      	percent(newPercent) {
		        if (newPercent >= 0 && !this.touch.initiated) {
		          	const barWidth = this.$refs.progressBar.clientWidth - progressBtnWidth;
		          	const offsetWidth = newPercent * barWidth;
		          	this._offset(offsetWidth)
		        }
	      	}
	    }
	}
</script>

<style scoped lang="less">
@import "~common/less/variable.less";

.progress-bar {
  height: 30px;
  .bar-inner {
    position: relative;
    top: 13px;
    height: 4px;
    background: rgba(0, 0, 0, 0.3);
    .progress {
      position: absolute;
      height: 100%;
      background: @color-theme;
    }
    .progress-btn-wrapper {
      position: absolute;
      left: -8px;
      top: -13px;
      width: 30px;
      height: 30px;
      .progress-btn {
        position: relative;
        top: 7px;
        left: 7px;
        box-sizing: border-box;
        width: 16px;
        height: 16px;
        border: 3px solid @color-text;
        border-radius: 50%;
        background: @color-theme;
      }
    }
  }
}

</style>